Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

BMS301 MEMBRANE RECEPTORS > RECEPTOR TYROSINE KINASES > Flashcards

RECEPTOR TYROSINE KINASES Flashcards

1
Q

What is a kinase?

A

An enzyme that catalyses the transfer (adition) of a phosphate group.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is a phosphatase?

A

An enzyme that catalyses the removal of a phosphate group.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What are the major classes of kinases? (2)

A
  1. Protein kinases

2. Lipid kinases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are the major amino acids that can be phosphorylated? (3)

A
  1. Serine
  2. Threonine
  3. Tyrosine
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Which part of an amino acid is targeted by kinases?

A

The hydroxyl group

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the distinction between tyrosine, serine and threonine kinases? And why?

A

Kinases that can phosphorylate serine and threonine cannot phosphorylate tyrosine, and vice versa. This is due to structural differences.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is a dual specificity kinase?

A

Can all on all three protein kinases.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What important roles do kinases play? (2)

A
  1. Signal transduction

2. Metabolic pathways

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Give examples of Receptor Tyrosine Kinases.

A 
EGFR
Insulin receptor
TrkA receptor
M-CSF receptor
FGFR
VEGF
Eph receptors
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the biomedical importance of receptor tyrosine kinases? (4)

A
  1. Important for regulating proliferation (oncogenic)
  2. Important for wound healing
  3. Important for angiogenesis
  4. Important for neuronal survival
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the easiest way to test whether a protein is important for a particular pathway?

A

Take away the gene (KO) and compare to the WT.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is a scratch assay?

A

Infliction of a wound with a pipette to scratch the surface of the epithelial layer to follow closure of the wound.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are FGF receptors important for?

A

Wound healing

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How many TMSD make up the structure of receptor tyrosine kinases?

A

1 TMSD (with the exception of the insulin receptor which has 2.)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What domains tend to make up RTKs? (3)

A
  1. Receptor tyrosine kinase domain
  2. Juxta membrane domain
  3. Tail
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What are the different types of kinase domains? (2)

A
  1. Continuous

2. Split by a kinase insert region

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Describe the diversity of the EC domains of RTKs.

A

Very diverse between the different types of receptors. Can include cysteine rich domains, immunoglobulin like domains etc with different numbers of repeats between the families. The diversity of the ligands that bind is reflected in the EC domains and motifs.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What are RTKs characterised by? (8)

A
  1. Cell surface receptors with intrinsic enzymatic activity (tyrosine kinases)
  2. Cytoplasmic domain has tyrosine kinase activity
  3. Mostly receptors for peptide/protein growth factors
  4. Regulate growth and differentiation and cell survival and many other processes
  5. Single TMSD (except insulin)
  6. Usually single polypeptide
  7. EC binding site often has immunoglobulin/fibronectin domains and many other domains
  8. IC domain includes tyrosines that can be cross phosphorylated.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is the fundamental problem of every ligand?

A

Transferring information from the outside of the cell to the inside of the cell.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

How are RTKs activated? (3)

A
  1. Ligand binding causes dimerisation/oligomerization
  2. Both EC and IC domains will come in close proximity of one another.
  3. Dimerisation/oligomerization allows cross phosphorylation on the IC side.
  4. Cross phosphorylation activates (increases the residual activity of) the tyrosine domains allowing docking sites for activation of downstream signalling. This can occur within the TK domain or in other domains eg tail or juxta.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What are the models for how ligands induce dimerisation? (4)

A
  1. TrkA ligand is itself a dimer and its two subunits require two receptors but there is no contact of the EC domains when they come together so the dimerisation is solely mediated by the dimeric ligand.
  2. Stem Cell Factor ligand is itself a dimer and contributes to the stabilisation of the dimer as well as causes a conformational change in the EC domain leading to direct contact between parts of the ligand binding domain.
  3. FGF ligand can be glycosylated and can play a role in ligand binding activity meaning ligand can be regulated as glycosylation is regulated. Ligand EC domains make contact through use of modified heparin.
  4. EGF is a monomeric ligand each ligand binding domain will bind EGF which will induce a change in domain structure which induces sticking and oligomerization. This is entirely mediated by the receptor.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is required for all kinases?

A

ATP

23
Q

Describe an activation loop. (2)

A
  1. The activation loops covers where the substrates would bind.
  2. Phosphorylation of the loop moves the loops for the substrate to bind and then be phosphorylated by ATP sitting in close proximity.
24
Q

If the kinase is inactive, how do you get phosphorylation in the first place?

A

There is an equilibrium and the activation loop is flexible to an extend that there are some binding sites accessible for spontaneous activation.

25
Q

What are MABs?

A

Monoclonal Antibodies

26
Q

How can we use MABs for RTKs?

A

The EC domains of RTKs cound be bound to MABs to prevent dimerisation and activation in the event of uncontrolled proliferation.

27
Q

Give an example of a MAB that can be used for RTKs.

A

Trastuzumab binding to the HER2 receptor as treatment for breast cancer.

28
Q

In RTKs what is the function of phosphorylation outside of the kinase domain?

A

Serves as recruitment for docking sites for signal transduction.

29
Q

What happens to RTKS when signalling occurs?

A

The RTKS reside on the PM and are endocytosed upon signalling to become part of the endosomal compartment.

30
Q

There is very little phosphorylation other than that of the activation loop that occurs in the tyrosine kinase domains? Why? (3)

A
  1. The tyrosine kinase sites must be freely accessible for the proteins that need to be phosphorylated so docking sites would inhibit accessibility.
  2. There is some movement associated with kinase activity which would not support binding with other domains.
  3. It is also not necessary as there are other domains that can serve as docking sites for a number of proteins.
31
Q

How do proteins bind specifically to phosphotyrosine?

A

SH2 domains are specialised in recognising phosphotyrosine.

32
Q

What are SH2 and SH3 domains?

A

Protein - protein interaction domains.

33
Q

Why is EGF different to other RTKs?

A

It is not activated by phosphorylation of the TK domain but allosteric activation.

34
Q

What is the downstream process of signal transduction for RTKs? (8)

A
  1. Phosphorylation in the C terminal and juxta membrane has an effect on Grb2.
  2. Grb2 is translocated from the cytosol to the vicinity of the PM.
  3. Grb2 has 2 SH3 domains which have affinity for Sos, it will translocate Sos to the PM.
  4. Grb2 also has an Sh2 domain which will bind to the phosphorylated receptor.
  5. Sos is an exchange factor; important for G proteins. G proteins are molecular switches cycling between active (GTP) and inactive (GDP) and Sos catalyses the exchange of GDP for GTP, thereby activating the G protein.
  6. The G protein is anchored by a lipid anchor to the PM.
  7. Sos can only find and act on Ras when it is also close to the PM because then it is in the vicinity of its substrate (Ras GDP).
  8. This means Sos translocation from the cytosol to the plasma membrane brings Sos in close proximity to Ras GDP.
35
Q

What is critical in the process of downstream signal transduction?

A

Correct localisation of proteins.

36
Q

What is the structure of Drosophila eye? (3)

A
  1. It is a compound eye.
  2. It is composed of many ommatidia.
  3. Each ommatidia is made up of 8 photosensitive cells.
37
Q

How are ommatidia arranged?

A

7/8 photosensitive cells are visible at the cell surface.

R8 is not visible.

38
Q

What effect does the Sevenless mutation have on the ommatidia?

A

R7 is missing.

39
Q

What effect does R8 have on R7 in ommatidia?

What happens in Sevenless mutation?

A

R8 plays a role in the induction of R7.
The R8 ligand (Boss) bind to R7 receptor (Sevenless) which elicits signal transduction which induces matures of the R7 precursor into the R7 neuron.

In Sevenless, there is no signalling from Sev RTK so no neuronal induction into a cone cell.

40
Q

How did they show that Ras was important in the pathway that leads to R7 fate in ommatidia?

A

They made a double mutant which was Sev- and a constitutive version of Ras.
The use of constitutively active Ras rescued cell fate and R7 became a neuron showing Ras is crucial in the pathways that leads to R7 cell fate.

41
Q

Describe the effectors of the Ras activated MAP kinase cascade.

A

Raf
Mek (a MAPKK)
MAPK

42
Q

Why is there a cascade if kinases rather than just one? (2)

A
  1. Each kinase has multiple effectors each having a specific set of substrates.
  2. Signal amplification
43
Q

Give an example of how signal amplification is important?

A

Blood clotting is a process that needs to happen quickly and so signal amplification means that each set of molecules activated will activate many more with an exponential response resulting in a cascade that will regulate gene expression.

44
Q

What is Cbl?

A

A ubiquitin ligase.

45
Q

What is the role of ubiquitin in the cell? (2)

A

It plays a major role in trafficking and degradation.

46
Q

How are RTKs trafficked?

A

Cbl binds to the phosphorylated site of the receptor.

The receptor is endocytosed and sorted for either degradation or recycling.

47
Q

What happens when mutations affect binding sites for Cbl?

A

If Cbl cannot bind, the receptor cannot be sorted to the lysosome for degradation and so will either continue to signal from the endosome or be recycled back to the PM for reactivation. This leads to increased signalling which increases transduction leading to increased proliferation which can lead to transforming potential rendering the molecule an oncogene.

48
Q

What is the role of EGF?

A

Promotes proliferation.

49
Q

What is the role of NGF?

A

Promotes differentiation of PC12 cells.

50
Q

What is a similarity between EGF and NGF signalling?

A

They both activate the Ras and MAPK pathways.

51
Q

Why is there a difference in cell fates causes by EGF and NGF signalling if they activate the same pathways?

A

Activation kinetics.
Both receptors undergo endocytosis but EGF is transported to the lysosome and degraded (shutting off signalling) whereas NGF receptors are predominantly recycled to the membrane.
Due to this transient vs sustained activation of the receptor this results in different activation of the bowtie network of positive and negative feedback loops meaning the output will differ.
NGF will cause neurite outgrowth.
EGF will cause cell proliferation.

52
Q

Describe the EGF pathway.

A

EGF undergoes ligand induced endocytosis and it transported to the lysosomes to be degraded thereby shutting off signalling.
EGF is ubiquitinated and sorted into ILVs of MVBs via HRS and ESCRT complexes I-III.
EGF activates ERK via the kinase RAF.
EGF activates the expression of MAP kinase specific phosphatases so called dual specificity phosphatases.
This will lead to dephosphorylation of ERK and will eliminate the positive ERK-RAF feedback loop.
At low levels of ERK activation FOS is rapidly degraded.

53
Q

Describe the NGF pathway.

A

NGF undergoes ligand induced endocytosis but is predominantly recycled to the PM.
NGF activates ERK and PKC. PKC phosphorylates RKIP (RAG kinase inhibitory protein( which will dissociate from RAF which can them be phosphorylated by ERK which will result in a positive feedback loop.
NGF stabilises FOS by ERK mediated and RSK2 mediated phosphorylation.
Sustained FOS activity results in induction of gene expression programmes that lead to differentiation and neurite outgrowth.
NGF leads to long lasting activation of Rap1 which activates BRAF.

BMS301 MEMBRANE RECEPTORS (2 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions